JPH11261529A - Code division multiple communications device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a code division multiple communications device which reduces the peak factor of data inputted to a sending amplifier and prevents unnecessary spurious radiation from occurring. SOLUTION: In this code division multiple communications device which multiplies transmission signals of plural channels by respectively different spread codes, and adds the data of plural channels thus acquired by a data adder 2 for subsequent transmission, a code which has the same number of 0s and -1s is used as each spread code, also an offset value 6 to reduce maximum amplitude is added to data 3 after addition and data 8 after adding the offset value is transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a code division multiplex communication device.

[0002]

2. Description of the Related Art As is well known, CDMA (code division multiplex).
The communication system is a wireless communication system in which a spread signal using different spreading codes is applied to a transmission signal composed of a plurality of channels, and the resulting spread spectrum signal composed of a plurality of channels is multiplexed and transmitted.
In this CDMA communication system, the crest factor, which is the ratio between the average power of the entire transmission signal and the instantaneous peak power, is:
Depending on the number of additions (multiplexes) of the spread spectrum signals, the crest factor is larger when the number of additions is larger than when it is smaller. Therefore, when the number of additions is large, a spread spectrum signal having a high crest factor may be generated instantaneously, and when this signal is input to the transmission amplifier, it becomes out of the transmission band due to the nonlinear characteristic of the transmission amplifier. Unnecessary spurs occur.

In order to prevent the generation of such unnecessary spurious components, linearity is guaranteed over a wide input range so that even a spread spectrum signal having a large amplitude can be amplified without causing nonlinear distortion. It is necessary to use a transmission amplifier. However, when such a transmission amplifier is used, there is a problem that the transmission amplifier becomes expensive and leads to a significant increase in cost.

[0004]

By the way, as a general means for preventing the generation of unnecessary spurious components as described above, an amplitude exceeding a certain value is limited so that a large amplitude is not input to the transmission amplifier. There was a peak clipping technique. Therefore, it is necessary to consider applying this peak clipping technique to a CDMA communication device. However, this peak clipping technology is
If the method is applied to the A-communication system, a limit is imposed on the amplitude value of the spread spectrum signal, which is originally meaningful, so that a correct value can be obtained when despreading the spread spectrum signal on the receiving side. Gone, received BER
(Bit error rate) is deteriorated.
For example, in communication using an 8-chip length spreading code,
When clipping is performed, a channel that obtains a value other than 8 at the time of despreading occurs.

The present invention has been made in view of the above-described circumstances, and provides a code division multiplex communication apparatus capable of reducing a crest factor of data input to a transmission amplifier and preventing generation of unnecessary spurious. It is intended to be.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a code division multiplex communication apparatus for multiplying data of a plurality of channels by different spreading codes, and adding and transmitting the resulting spread spectrum signals of the plurality of channels. A code having the same number of 0 and -1 is used as each of the spread codes, and an offset value for reducing the maximum amplitude is added to the data obtained by adding the spread spectrum signals of the plurality of channels and transmitted. The gist of the present invention is a code division multiplex communication device characterized by the following.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a multiplexing circuit of a CDMA communication device according to an embodiment of the present invention. This CDMA communication apparatus is used in a mobile communication base station using the CDMA system.

In FIG. 1, a data adder 2 has a channel CH1.
This is means for adding data 1 (spread spectrum signal) for seven channels consisting of .about.CH7. Each data 1 to be added by the data adder 2 is a spread spectrum signal. In a spreading section (not shown) at the previous stage of the multiplexing circuit, input data corresponding to each channel is added to each channel. Is obtained by multiplying by the spreading code specified in.

Here, with reference to FIG. 2, the processing contents of this diffusion unit will be described. FIG. 2A illustrates spreading codes for seven channels used in the spreading unit in the present embodiment, and FIG. 2B illustrates input data for seven channels before spreading. Here, the start time of the spread code, the start time of the input data, the length of the spread code, and the length of the input data are the same. In this embodiment, each channel uses a spreading code having a length of 8 chips and spreads the spectrum of each input data at a spreading factor of 8 times.

In this embodiment, as shown in FIG. 2 (a), each channel uses a spreading code having the same number of +1 and -1. The use of a spreading code that satisfies such a condition is because when a spread spectrum signal is generated and transmitted using a spreading code that does not satisfy the condition, when the despreading of the spread spectrum signal is performed on the receiving side, it will be described later. This is because the value obtained by multiplying the spreading value by the spreading code does not become 0, and a correct despreading result cannot be obtained. This will be described later.

[0011] The spreading section performs spectrum spreading by multiplying the input data corresponding to each channel by each spreading code described above. FIG. 3A shows a spread spectrum signal corresponding to each channel obtained as a result, that is, data 1 of each channel to be added by the data adder 2. FIG. 3B shows data 3 obtained by adding these data 1 by the data adder 2.

The peak value detection circuit 4 is supplied with the added data 3 obtained from the data adder 2 and a clock 5 synchronized with the symbol. Here, the supply timing of the clock 5 is synchronized with the supply timing of the data 3 after the addition. This clock 5 can be easily extracted from the clock generator of the base station.

The crest value detection circuit 4 captures the added data 3 by the clock 5 and detects the maximum value and the minimum value of the added data 3. In this embodiment, since the spreading code is 8 chips long, the 8 chips length is set as one unit,
The maximum value and the minimum value of the data 3 are detected within the 8-chip length.
Therefore, in the example shown in FIG. 3B, the maximum value of the data 3 is 5 and the minimum value is -3.

Then, the peak value detecting circuit 4 calculates the offset value 6 by the following equation using the maximum value and the minimum value obtained as described above. Offset value = -1 x (maximum value + minimum value) / 2

As shown in FIG. 3B, when the maximum value of data 3 is 5 and the minimum value is -3, the offset value 6 becomes Becomes

The offset value adder 7 includes a data adder 2
Then, the offset value obtained by the peak value detection circuit 4 is added to the added data 3 obtained from the above, and the addition result is supplied as transmission data 8 to a transmission unit (not shown). FIG.
Shows transmission data 8 after adding an offset value 6 (= -1) to the added data 3 shown in FIG. 3B. The absolute value of the maximum amplitude of the data before addition of the offset value (data 3 after addition) shown in FIG. 3B is 5, whereas the absolute value of the maximum amplitude of the data after addition of the offset value shown in FIG. It can be seen that the absolute value has decreased to 4. The transmission data 8 whose absolute value of the maximum amplitude has been reduced by the offset value adder 7 is transmitted to the transmission unit, amplified by the transmission unit, and transmitted to the outside.

The data adder 2 can be easily constituted by a combination of generally available basic logic ICs, and the offset value adder 7 has a part of the function of the data adder 2. Can be configured. In addition, the peak value detection circuit 4 is required to have a function of finding the maximum value and the minimum value from the added data 3 and calculating the offset value, but can be easily realized by using a configuration having a CPU and software. can do.

Next, the receiving process of the transmission data 8 on the receiving side will be described with reference to FIG.

On the receiving side, when the transmission data 8 is received, the received data is despread. This despreading is performed by multiplying, on a chip basis, a spreading code corresponding to a desired channel among spreading codes (see FIG. 2A) corresponding to each channel used for spreading on the transmitting side in chip units. This is done by summing the results.

FIG. 5 shows a waveform obtained as a result of multiplying the received data (the same waveform as the transmission data 8 shown in FIG. 4) by the spread code corresponding to CH1 on a chip-by-chip basis. In the case of this example, the despread result corresponding to CH1 is +8
Becomes Therefore, by dividing the despread result +8 by the number of chips 8, the data of CH1 “+
1 "is demodulated.

As described above, according to the present embodiment, despite the fact that the offset value is added to the transmission data 8 transmitted from the transmission unit, the receiving side receiving the offset value does not add the normal offset value. By performing the same despreading as in the case of data, the original input data corresponding to the desired channel can be demodulated.

Hereinafter, this will be described more specifically using mathematical expressions. First, the input data corresponding to each channel is B1 to B7, the spreading code is W1 to W7, and the offset value is D. In this case, the data 1 of each channel after spreading input to the data adder 2 is B1
× W1, B2 × W2,..., B7 × W7. Therefore,
Data 3 after addition is data 3 after addition = B1 × W1 + B2 × W2 + B3 × W
3+... + B7 × W7.

It is assumed that the offset value is not added to the data 3 and that the data 3 is transmitted from the transmitting unit as it is. It is also assumed that the receiving side receives the data 3 and demodulates the input data corresponding to CH1 from the data 3. In this case, the receiving side multiplies the data 3 by W1 as shown in the following equation. W1 (B1 × W1 + B2 × W2 + B3 × W3 +... + B7
× W7) = W1 × W1 × B1 + W1 × W2 × B2 + W1
× W3 × B3 +... + W1 × W7 × B7

Here, from the orthogonality of the spreading code, W1 × W2 = W1 × W3 = W1 × W4 =... = W1 × W7
= 0 W1 × W1 = 1. Therefore, the result of the above multiplication is: W1 × W1 × B1 + W1 × W2 × B2 + W1 × W3 × B
3+... + W1 × W7 × B7 = B1, and the original input data B1 corresponding to CH1 is obtained.

Next, the operation of this embodiment will be described.
First, in the present embodiment, the sum of the data 3 after the addition and the offset value 6 (= D) is transmitted as the transmission data 8, so that the transmission data 8 = B1 × W1 + B2 × W2 + B3 × W3 +
.. + B7 × W7 + D.

If it is assumed that the receiving side receives, for example, data of CH1, the receiving side performs despreading as shown in the following equation. W1 (B1 × W1 + B2 × W2 + B3 × W3 +... + B7
× W7 + D) = W1 × W1 × B1 + W1 × W2 × B2 +
W1 × W3 × B3 +... + W1 × W7 × B7 + W1 × D

Also in this case, as described above, W1 × W2 = W1 × W3 = W1 × W4 =... = W1 × W7 due to the orthogonality of the spreading code.
= 0 W1 × W1 = 1.

Further, since the spreading code W1 is a code in which the numbers of +1 and -1 are equal, W1 × D = 0.

Therefore, the result of the above multiplication is: W1 × W1 × B1 + W1 × W2 × B2 + W1 × W3 × B
3+... + W1 × W7 × B7 + W1 × D = B1. The same applies to despreading when receiving another channel.

As described above, in the present embodiment, since the transmitting side performs spreading using spreading codes having the same number of +1 and −1, even if a signal obtained by adding an offset value to this is transmitted. The effect of the offset value does not appear on the result of the despreading on the receiving side.

Therefore, according to the present embodiment, on the transmitting side, the offset value is added to the multiplexed spread spectrum signal to reduce the crest factor of the added data 3, thereby preventing the generation of unnecessary spurious. This can be prevented, and even if the offset value is added in this manner, the receiving side can perform the same despreading as before and receive data of a desired channel.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this. For example, the following modifications may be made to the above embodiment. (1) In the above embodiment, the offset value is calculated in the unit of the spread code length, but may be calculated in the unit of a data length that is an integral multiple of the spread code length. (2) In the above embodiment, the maximum value and the minimum value of the data after the addition are detected, and the offset value is calculated by the calculation of the offset value = −1 × (maximum value + minimum value) / 2. The calculation method is not limited to this. In short,
It suffices if the maximum amplitude of the added data can be reduced to such a degree that unnecessary spurious does not occur in the transmission amplifier. Therefore, the offset value added to the data after the addition may be smaller than the offset value obtained by the above equation, as long as unnecessary spurious noise can be prevented.

[0033]

As described above, according to the present invention, a signal having a large instantaneous amplitude contained in an input signal to a transmission amplifier of a code division multiplex communication apparatus is reduced by adding an offset value. There is an effect that unnecessary spurious is not generated in the transmission amplifier.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a multiplexing circuit of a code division multiplex communication device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a spread code and input data according to the embodiment;

FIG. 3 is a diagram exemplifying data 1 corresponding to each channel after spreading and data 3 after addition in the embodiment.

FIG. 4 is a diagram exemplifying data 8 after adding an offset value 6 to data 3 after addition in the same embodiment.

FIG. 5 is a diagram exemplifying a result of despreading on the receiving side of CH1 in the embodiment.

[Explanation of symbols]

 1 Data of each channel after spreading 2 Data adder 3 Data after addition 4 Peak value detection circuit 5 Clock synchronized with symbol 6 Offset value 7 Offset value adder 8 Transmission data

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[Procedure amendment]

[Submission date] April 2, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

SUMMARY OF THE INVENTION The present invention relates to a code division multiplex communication apparatus for multiplying data of a plurality of channels by different spreading codes, and adding and transmitting the resulting spread spectrum signals of the plurality of channels. A code having the same number of +1 and -1 as each spreading code, and adding an offset value for reducing the absolute value of the maximum amplitude to the data obtained by adding the spread spectrum signals of the plurality of channels. The present invention provides a code division multiplex communication apparatus characterized in that the transmission is performed after the transmission.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this. For example, the following modifications may be made to the above embodiment. (1) In the above embodiment, the offset value is calculated in the unit of the spread code length, but may be calculated in the unit of a data length that is an integral multiple of the spread code length. (2) In the above embodiment, the maximum value and the minimum value of the data after addition are detected, and the offset value is calculated by an operation of offset value = −1 × (maximum value + minimum value) / 2. The calculation method is not limited to this. In short,
It suffices if the absolute value of the maximum amplitude of the added data can be reduced to the extent that unnecessary spurious noise does not occur in the transmission amplifier. Therefore, the offset value added to the data after the addition may be smaller than the offset value obtained by the above equation, as long as unnecessary spurious noise can be prevented.

Claims (3)

[Claims] 1. A code division multiplexing communication apparatus for multiplying data of a plurality of channels by different spreading codes, adding the resulting spread spectrum signals of the plurality of channels, and transmitting the resultant data. And using a code having the same number as -1 and -1 and adding an offset value for reducing the maximum amplitude to the data obtained by adding the spread spectrum signals of the plurality of channels and transmitting the data. Multiplex communication device. 2. The code division multiplex communication device according to claim 1, wherein the offset value is calculated in units of a code length of the spreading code. 3. The method according to claim 1, wherein a maximum value and a minimum value of the data after the addition are detected, and the offset value is calculated by an operation of: offset value = −1 × (maximum value + minimum value) / 2. Item 3. The code division multiplex communication device according to item 1 or 2.